Drive recorders are known that record images acquired from vehicle-mounted cameras. For these drive recorders, a period during which images can be saved is limited by the capacity of memory available for recording images. This period decreases with increasing number of cameras intended for the recording.
PTL 1, for example, describes a technique for preventing unwanted images from being recorded in the memory. According to PTL 1, when a vehicle is parked or stopped and its engine is turned off, the drive recorder enters a monitor mode in which the surroundings are monitored for obstacles approaching or coming into contact with the vehicle. In the monitor mode, when an ultrasonic sensor detects an obstacle within a predetermined range, the drive recorder starts recording images from the vehicle-mounted camera.